Fixed refcount on setting array to nulable property
Fixed refcount on setting array to nulable property

Refs: #1915, #1918, 1f6962d#commitcomment-35331987

/cc @chrysanthemum

dreamsxin/zephir,dreamsxin/zephir,dreamsxin/zephir,dreamsxin/zephir,dreamsxin/zephir,dreamsxin/zephir